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LQ1 CPS.


jiggity76

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Hey guys, I been looking thru some old threads and can't find anything on replacing the crank position sensor on the LQ1's.  I've even looked thru my manuals and nothing is listed for the procedure.

Any ideas on how to do this?  I want to rule out the sensor.  Do I need to pull the right front tire to get better access to it or go up from below?  Thanks guys!

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I’ve done this job. It’s a bugger because of the lack of space between the firewall and engine.  Can’t get at it from the wheel well; knock sensor, but not the crank. There is a test for the crank sensor itself.  You can unplug the harness at the ignition module to complete the test, but I cant say what the test itself is. An analogue ohmmeter while cranking the engine sounds familiar though. I have the dealer manuals so can take a look and see if it’s in there later. Best do this first to make sure your not wasting your time. If your car won’t start and you don’t have spark this could be your trouble. Bad ICMs seem to be intermittent.


To change the sensor:

- Get the car up nice and high on jack stands.  You need to work from underneath with your feet out the front.

- clean the bejesus out of the area before you start and shine up there with lots of light. 

- use a very long flat screw driver to carefully open the locking tab on the harness, don’t break the tab.  While it’s open use a pair of very long locking pliers to jiggle the harness off. I’ll post a pic of the tool i used. I would not have been able to do this job without it.

- I believe a 7mm (maybe an 8mm) bolt holds the sensor into the block. Use a ratcheting wrench and tape an extension to it. I think it worked better to tape on the inside half way down but might take a few try’s.

- use the locking pliers to pull the sensor out, make sure the o-ring makes it in one piece.

- like most jobs installation is the reverse of removal.

Hardest part is getting the bolt back in.  I fought with it for quite a while and ended up using  a 1/8” piece of welding rod with 3/4” bent at a 90 on one end to line the sensor bolt hole up with the threads in the block. You just put the 90 in the crank bolt hole and spin the sensor until you feel the 90 drop into the threaded hole in the block.  Rock it back and forth in your fingers to find best centre and the bolt should start first try. I fought getting the bolt in for a long time and had it land on my face a few times, wasn’t able to get it in without this little home made tool.

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Edited by GTP091
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Oh man, that sounds really intimidating.  Yes, I feel like going up from below is the best way.  I've also just recently heard about going over the transmission on the passenger side and trying it that way.  My car is an automatic by the way.

I just want to change it out and eliminate it as it's sort of my last resort before I take it into the dealer.  I'm also going to replace the MAP sensor since it's not a big deal doing that one.  

It's currently up on jack stands so that part is already done, LOL.  Thanks so much for the very detailed process and these tips.  I very much appreciate it and going to tackle it tomorrow.  

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I’ve just posted the pics of the pliers above. Hope you can find em somewhere and hope you can get it done on your own. You’ll feel like a doctor doing surgery without being able to touch the piece you’re working on. Your hand won’t fit up there at all.  A shop might tell you some nonsense on not wanting work on it as soon as they see in there. Not likely many mechanics have done this job lately. The book might even tell them to lower the cradle. Not necessary!

Edited by GTP091
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Anyone ever try to replace the LQ1 crank sensor from the top, with the cylinder head and intake manifold removed?

I did a valve job on my '93 years ago, the knock sensor is real easy to get at, and I poked a block heater and alternator in at the same time because access is real good with the head gone.  Didn't even look for the crank sensor; never occurred to me to dick with it.

I still haven't gotten the '92 running; I bet it's been parked for six years or more.  It's on the "List of Things to Do" for this summer--and part of that will be to valve-job the thing.  So intake and exhaust manifolds will be gone, both heads and cam carriers removed, etc.

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1 hour ago, GTP091 said:

I’ve just posted the pics of the pliers above. Hope you can find em somewhere and hope you can get it done on your own. You’ll feel like a doctor doing surgery without being able to touch the pie you’re working on. Your hand won’t fit up there.  A shop might tell you some nonsense on not wanting work on it as soon as they see in there. No likely many mechanics have done this job lately. The book might even tell them to lower the cradle. Not necessary!

I feel it's fate that you responded to me!  I actually bought some really nice, long pliers last Fall for just this sort of thing!  I have different sizes/lengths and curvatures. 

I was thinking that maybe I could go in from the top?  You see, I would also like to replace the coolant temp sensor and most likely will have to pull the plenum to get to it.  I've done this before and getting quite good at it.  If need be, I could also remove the spark plug wires, etc and see if I could get between the motor and the firewall?  Just wondering and typing out loud.  Or do you think that won't help and just go with the original idea of going up from below?

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1 hour ago, Schurkey said:

Anyone ever try to replace the LQ1 crank sensor from the top, with the cylinder head and intake manifold removed?

I did a valve job on my '93 years ago, the knock sensor is real easy to get at, and I poked a block heater and alternator in at the same time because access is real good with the head gone.  Didn't even look for the crank sensor; never occurred to me to dick with it.

I still haven't gotten the '92 running; I bet it's been parked for six years or more.  It's on the "List of Things to Do" for this summer--and part of that will be to valve-job the thing.  So intake and exhaust manifolds will be gone, both heads and cam carriers removed, etc.

My poor International has been sitting since 2009.  I've had it since Dec of 15.  I've been working on it pretty steady in that time frame, just slow and only when I can afford too.  I'm thinking about trying from the top as well.  I need to do the coolant temp sensor and will most likely have to pull the plenum at least.  Not sure if that will give me any room but just a thought.

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I've posted before about CPS sensors.
Imho, *ONLY* use one that you buy, in person, from a local dealership!
You've been warned.  :)
If people want to lay Russian Roulette, that is their choice.
Iirc, even a "Standard (brand name)" from Rock Auto didn't last long.  And, imho, the Standard (brand) is often better than the GM OEM stuff.  Maybe it was one of the many counterfeits?

Just my two cents. :)
I've been happy with my local GM Dealer bought CPS now for many years.  Before that, within ~6 months, I'd have the occasional "no start" pita issue that often happens with failing CPS sensors.
Btw, I have TECH-II scanner (?possible clone?).  So, I do a CPS calibrate when I change the sensors.

Good Luck!

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6 minutes ago, Cutlass350 said:

I've posted before about CPS sensors.
Imho, *ONLY* use one that you buy, in person, from a local dealership!
You've been warned.  :)
If people want to lay Russian Roulette, that is their choice.
Iirc, even a "Standard (brand name)" from Rock Auto didn't last long.  And, imho, the Standard (brand) is often better than the GM OEM stuff.  Maybe it was one of the many counterfeits?

Just my two cents. :)
I've been happy with my local GM Dealer bought CPS now for many years.  Before that, within ~6 months, I'd have the occasional "no start" pita issue that often happens with failing CPS sensors.
Btw, I have TECH-II scanner (?possible clone?).  So, I do a CPS calibrate when I change the sensors.

Good Luck!

Thanks man!  This is what I did.  I got the part # from my book, called my local GM dealer and verified that it was the right part #, they looked it up in their system and didn't have one in stock.  They did however give me another GM dealers info and I called them.  They did have it in stock and they shipped it too me.  I very much try to get NOS parts for both of my W's.

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19 minutes ago, jiggity76 said:

I feel it's fate that you responded to me!  I actually bought some really nice, long pliers last Fall for just this sort of thing!  I have different sizes/lengths and curvatures. 

I was thinking that maybe I could go in from the top?  You see, I would also like to replace the coolant temp sensor and most likely will have to pull the plenum to get to it.  I've done this before and getting quite good at it.  If need be, I could also remove the spark plug wires, etc and see if I could get between the motor and the firewall?  Just wondering and typing out loud.  Or do you think that won't help and just go with the original idea of going up from below?

The crank sensor is not to far up the block when looking at it from the bottom.  I’d think the exhaust manifold and down pipe would be completely in the way to go in from the top.  Never tried so can’t say it wouldn’t work but I would be surprised if it was easier. I’d think its even tighter up top.

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43 minutes ago, GTP091 said:

The crank sensor is not to far up the block when looking at it from the bottom.  I’d think the exhaust manifold and down pipe would be completely in the way to go in from the top.  Never tried so can’t say it wouldn’t work but I would be surprised if it was easier. I’d think its even tighter up top.

That makes sense now that you mentioned it.  I was just wondering, thank you. 

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On 3/10/2021 at 9:37 PM, GTP091 said:

Is this issue on your International?  What are the symptoms? Sudden no start or gradual worsening?

I was thinking that it was but I'm getting spark from the coil packs so it must be sending a signal and working.

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Posted (edited)
2 hours ago, GTP091 said:

Is it a miss you have or generally rough running?  If it’s a miss, you may want to check the coils, wires, etc. 

No, she's not running yet.  She's trying to start but goes right back to just cranking over.  She has a rhythm to her, wants to try and start but then goes right back to just cranking over.  Not sure how to explain it exactly.  I have confirmed she's getting fuel and fire.  I can smell the exhaust/fuel being burned.  I put in new injectors, fuel pump, ignition module/coil packs, and new plugs/wires.  I really think it's a timing issue with either the belt or chain.  She's going to the dealer soon for a proper diagnosis.

Edited by jiggity76
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If you think a dealer will be of much help I have some oceanfront property in Nebraska. Most techs there if they aren't parts changers were only born when the car was new. OBD 1 may as well be hieroglyphics to them

I've done a number of them. I'll be honest I'm hard pressed to think of a worse job on an Automatic LQ1 car.

Step one, pull the alternator, that will give you the best access to it

Step two, pray to whichever greater power you prefer that it comes out without a fight. Oftentimes they will split down the side, oil will get inside and the body will expand and get stuck in the bore. Absolute nightmare to get them out after that. It quickly goes from "lets remove the bolt and pull this out to" Def-con 5  prying and breaking out out piece by piece.

My old Euro 3.4 I had to have messed with that stupid thing for a few weeks back in the day. I ended up getting a dremel back there with a drillbit and ripped it out with a drywall screw and vice grips. 

By the way did you ever verify timing?

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21 minutes ago, White93z34 said:

If you think a dealer will be of much help I have some oceanfront property in Nebraska. Most techs there if they aren't parts changers were only born when the car was new. OBD 1 may as well be hieroglyphics to them

I've done a number of them. I'll be honest I'm hard pressed to think of a worse job on an Automatic LQ1 car.

Step one, pull the alternator, that will give you the best access to it

Step two, pray to whichever greater power you prefer that it comes out without a fight. Oftentimes they will split down the side, oil will get inside and the body will expand and get stuck in the bore. Absolute nightmare to get them out after that. It quickly goes from "lets remove the bolt and pull this out to" Def-con 5  prying and breaking out out piece by piece.

My old Euro 3.4 I had to have messed with that stupid thing for a few weeks back in the day. I ended up getting a dremel back there with a drillbit and ripped it out with a drywall screw and vice grips. 

By the way did you ever verify timing?

Thanks Chris.  I was just telling another member about this today.

I have two dealers in my area that have confirmed they know these old LQ1's.  One tech has been with the same dealer for 24 yrs now.  When I talked to him, I wanted him to understand that I have a DOHC 3.4, not a pushrod 3.4.  He simply replied, "man, I haven't seen one of those in awhile but yes, same motor as the Z34's".  He was also excited knowing it was in a Cutlass Supreme International coupe.  "I would love a shot at it", he also replied.

Tech #2 at a different local GM dealer just recently worked on a white 92 Z34.  After talking with him, he has serviced this same car for about 10 yrs now.  He also wants to see an International coupe and excited to see it.  

This is what I have done and 2 other members have done with the timing.  Took the cog covers off, verified the belt is in good shape and possibly new.  We also verified the belt does move when turning the motor over.  I feel the timing is off either thru the belt being done due to a belt failure before I got the car or the chain has skipped or stretched.  Again, the belt on the car looks brand new and may have been put on wrong when the one before it either broke or was replaced for maintenance.  

I'm not going to mess with the CPS until I hear back from the dealer diagnostic.  Not going to replace something if it isn't broke.  Also, I believe the CPS is working as I'm getting fuel and ignition.  I can smell the and hear the motor attempting to start, just not in the right time.  Both dealers have quoted me $115 bucks to do a full diagnostic on it so I figured, what the Hell.

If the CPS is the culprit, I'm pulling the motor.  I have a brand new hoist, stand, and the place/time to do it.  It would also be a good time to clean everything up, replace the alternator and what not.  The engine bay could use a good scrubbing and paint touch up as well.  I'm not scared to get dirty and work.  Done it before.

 

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Greg:

this does sound like it might be a map issue, your description of the symptoms sort of point in that direction. If there is a map issue the ecm cannot configure the proper fuel mixture to get the engine to fire. Is there a check engine light on at all?.......(other than the usual code 12 when one turns the key to run)

A faulty ecm coolant temp sensor sensor circuit can trigger a map issue. One needs a scanner to read (in real time) what the koeo reading for the ect circuit is (example...-49 degrees fahrenheit with the key on), that is an indicator that the ecm is not seeing the proper ambient temp the ect circuit should be supplying.

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1 hour ago, 55trucker said:

Greg:

this does sound like it might be a map issue, your description of the symptoms sort of point in that direction. If there is a map issue the ecm cannot configure the proper fuel mixture to get the engine to fire. Is there a check engine light on at all?.......(other than the usual code 12 when one turns the key to run)

A faulty ecm coolant temp sensor sensor circuit can trigger a map issue. One needs a scanner to read (in real time) what the koeo reading for the ect circuit is (example...-49 degrees fahrenheit with the key on), that is an indicator that the ecm is not seeing the proper ambient temp the ect circuit should be supplying.

You know what, I HAVEN'T changed the MAP sensor yet and I already have a brand new NOS one so why not.  Thank you for jogging my memory.  That's something I'm definitely going to do.  I also have a coolant temp sensor, again, brand new and NOS.  I wasn't really thrilled about pulling the plenum off again as it looks kinda tight in that area but I would have to pull the plenum anyways to do any timing work and the dealer would have to do the same.  I'll give it a shot.

Do these MAP sensors fail often?  The one that's on the car is also a GM one, it has it stamped on the cover.  Maybe it's the original one and with 153,000 miles, it very well might be and has failed.

Yes, I do have a "service engine soon" light on the cluster when I turn the car on.  The ECM is alive.

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1 hour ago, 55trucker said:

Greg:

this does sound like it might be a map issue, your description of the symptoms sort of point in that direction. If there is a map issue the ecm cannot configure the proper fuel mixture to get the engine to fire. Is there a check engine light on at all?.......(other than the usual code 12 when one turns the key to run)

A faulty ecm coolant temp sensor sensor circuit can trigger a map issue. One needs a scanner to read (in real time) what the koeo reading for the ect circuit is (example...-49 degrees fahrenheit with the key on), that is an indicator that the ecm is not seeing the proper ambient temp the ect circuit should be supplying.

This would also give me a chance to put on my new FPR as well.

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